A review is given of the various concepts offracture mechanics ,furthermore of their application to assess thetoughness of steels and to guarantee the safety of structurescontaining cracks .The three most important parameters are thestress-intensity factor Kl for linear elastic fracture mechanics(LEFM) ,the crack tip opening displacement CTOD and the J-integral for elastic-plastic fracture mechanics (EPFM) .TheASTM designation E 1820-696 provides a common method fordetermining all applicable toughness parameters from a singletest ,including R-curves .Many investigations dealt with thenumerous influences on these parameters ,e.g. specimengeometry and temperature and strain rate .Various failureconcepts have been developed .The method of LEFM based onplane strain fracture toughness Klc is well established for highstrength steels or low temperatures .For modern steels with hightoughness the more complicated concepts of EPFM have to beapplied .Because of the availability of commercial software forFE-calculations the application of Jintegral has becomewidespread in recent years .A number of approximative methodshas been elaborated ,e.g. CTOD-design-curve ,BSIPD6493:1991 ,CEGB-R6-method ,ETM, Eurocode 3Annex C.Although the theory of fracture mechanics regards the material asan isotropic continuum the question is of great importance ,howits materials parameters depend on the microstructure of thesteels .Systematic investigations with the aid of the hotdeformation simulator Wumsi showed the favourable materialproperties of fracture mechanics resulting fromthermomechanical treatment .Many models were published forthe quantitative correlation between microstructure andtoughness parameters ,mainly Klc .At the moment the modifiedGurson model is in widespread use ,which allows the prediction of J-Rcurves.
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